The present invention relates to resistance welding apparatus and more particularly to a lightweight, portable spot resistance welding device.
In resistance spot welding, electrode pressure is used to force the two pieces together. Heat, generated by the resistance of the workpieces to the flow of electricity, either melts the material at the interface, or at least makes it plastically adhesive. When the flow of current stops, the electrode force is further maintained for a fraction of second, while the weld rapidly cools and solidifies.
There are two types of welding equipment: Direct energy machines and stored energy machines. The stored energy mode is usually preferred because it is a more efficient and a more controlled process than the direct energy mode, and causes less extra heating, oxidation and deformation of the workpieces.
In principle, the stored energy welding machine extracts energy from the power line over a period of time and stores it in a high voltage capacitor's bank. The stored energy is discharged through a pulse transformer which converts the high voltage pulse into the required high current pulse (at low voltage) which is delivered by highly conductive cables to the welding head and passes through the workpiece. A third cable runs from the supply to the welding head and ensures that the firing switch of the discharge will close only after the two electrode are pressed together against the workpiece.
Commercial stored energy power supplies have a peak output voltage of 6 to 10 Volts and deliver up to several hundred Joules during a pulse (or two pulses) which can have a duration of several milliseconds. Typical weight of supplies range in 15 to 30 kg. Even portable battery powered light duty welding power supplies have a typical weight of about 10 kg.
Thus, no truly portable resistance welding system exists in a sense that the complete welding system can be conveniently carried and operated by the operator; or without being connected to the supply by heavy duty welding cables in the direct energy mode.